1. Field of the Invention
The present invention relates to coating paper for printers. The invention particularly relates to coating paper for ion deposition printers which employ dry magnetic toner.
2. Discussion of the Prior Art
A number of conventional printers and copiers employ dry magnetic toner.
Ion deposition high speed printers, for example; as disclosed in U.S. Pat. No. 4,409,604, are in conventional use as computer mainframe printers or in other service such as the printing of tags and labels.
These printers normally employ dry magnetic toner to form a toned latent image transferrable from the printer's dielectric imaging cylinder to receiving paper. In practice, in order to obtain the best print quality and toned image density, heat fusing equipment is often employed within the printer. The toned latent image on the dielectric imaging cylinder is subjected to heat fusing immediately after transfer whereupon the toned image is heat fused to the receiving paper. While the process of heat fusing improves print quality, it involves expensive heating equipment within the printer and added operational complexity. It has thus been an objective in this art to eliminate the heat fusing equipment without sacrifice in image density and print quality. In addition to eliminating the heat fusing step, it has also been a long standing objective to improve the smudge resistance of the transferred toned image on the receiving paper.
Dry magnetic toners normally require heat and pressure to melt fuse the particles to the substrate being printed. These toners comprise thermoplastic resin binders, colored pigment and magnetic additives or charge control agent. The toner described in U.S. Pat. No. 4,528,257 is representative of this type which employs a crystalline resin with a glass transition temperature (T.sub.G) of 45.degree. C. to 90.degree. C. and an immiscible amorphous resin component with a T.sub.G of 10.degree. C. higher than the crystalline resin. U.S. Pat. No. 4,508,257 represents an attempt to improve print quality and to permit faster printing speeds with reduced fusion temperatures. Heretofore, cold pressure fixing of a dry magnetic toner image on plain, coated or impregnated papers does not fully compare in print quality to that offered by heat fusion or alternate printing means such as thermal. Cold pressure fixing systems were developed to eliminate heat fusing and associated fire hazards, to reduce warm up time and lower the system's overall energy requirements. However, cold pressure fixing normally requires high nip pressures (well above 100 pounds/linear inch) which increases paper gloss and results in a glossy black image.